1. Field of the Invention
This invention relates to novel bridged indicator dyes. In another aspect it relates to photography and, more particularly, to photographic processes and products wherein the novel bridged indicator dyes are employed as optical infrared filter agents to protect a selectively exposed photosensitive material from further exposure during processing in ambient light.
2. Description of the Relevant Art
Photographic processes for producing both black-and-white and color images in which development of the light-sensitive photographic material is conducted outside of the camera in the presence of ambient light are now well known. Of particular interest in such photographic processes are diffusion transfer systems wherein the image-receiving layer carrying the transfer image is not separated from the developed photosensitive layer(s) after processing but both components are retained together as a permanent integral laminate, the final image being viewed through a transparent (support) element against a reflective, i.e., white, background. Such systems are described, for example, in U.S. Pat. Nos. 3,415,644, 3,415,645 and 3,415,646 issued Dec. 10, 1968 to Edwin H. Land.
These systems generally employ a light-absorbing material or optical filter agent in the processed film unit together with a layer of a light-reflecting material, preferably titanium dioxide, to protect the selectively exposed silver halide emulsions from post-exposure fogging during development in ambient light. The optical filter agents absorb light from a specific region of the spectrum thereby preventing or at least inhibiting light of that specific region from reaching and exposing the light-sensitive layer. The concentrations of optical filter agent and light-reflecting material required to provide adequate protection of the photosensitive layer(s) will vary with the process being performed and the anticipated conditions, e.g., light intensity, dark time, etc. and may be readily determined for any photographic process by routine experimentation.
In a preferred embodiment, the optical filter agent is a pH-sensitive dye, i.e., a dye possessing spectral absorption characteristics that are reversibly alterable in response to changes in environmental pH and particularly, a pH-sensitive dye having a colored or light-absorbing form above a given alkaline pH and a colorless or non-light-absorbing form below said pH. Such pH-sensitive dyes are frequently referred to as indicator dyes.
Various pH-sensitive dyes have been disclosed as light-absorbing optical filter agents. Examples of such indicator dyes found to be particularly useful for protection in the visible region of the spectrum are the phthaleins, i.e., the phthalide and naphthalide dyes derived from indoles disclosed in U.S. Pat. No. 3,702,244 issued Nov. 7, 1972 to Stanley M. Bloom, Alan L. Borror, Paul S. Huyffer and Paul T. MacGregor, and the phthalide and naphthalide dyes derived from phenols and 1-naphthols disclosed in U.S. Pat. No. 3,702,245 issued Nov. 7, 1972 to Myron S. Simon and David P. Waller. As discussed in the latter patent, phenol and 1-naphthol phthaleins especially useful for photographic processes employing highly alkaline media are those possessing a hydrogen-bonding group, for example, a carboxy group ortho to the p-hydroxy group of the phenol or naphthol radicals. As discussed in these and other patents, the 1-naphthol or phenol phthaleins are generally used in combination with the indole phthaleins where it is desired to provide protection from post-exposure fogging throughout the visible spectrum.
U.S. Pat. No. 4,886,733 issued Dec. 12, 1989 to Myron S. Simon discloses unsubstituted phenanthrol/o-carboxynaphthol phthaleins which provide opacification extending into the far red and near infrared. Substituted phenanthrol/o-carboxynaphthol phthaleins are disclosed in U.S. Pat. No. 4,891,298 issued Jan. 2, 1990 to David P. Waller which also absorb into the far red and near infrared (.lambda.max.apprxeq.680 nm) but which possess a broader absorption spectrum and absorb incident radiation more strongly at the longer wavelengths than the unsubstituted phenanthrol/o-carboxynaphthol phthaleins and di-(o-carboxynaphthol) phthaleins. Additionally, they show increased absorption in the blue and green region of the spectrum.
In photographic systems where the silver halide light-sensitive emulsion has been optically sensitized to the longer wavelength infrared region, e.g., systems which electronically expose a spectrally sensitized photosensitive element with infrared radiation emitted from a semiconductor laser or LED, pH-sensitive opacification dyes which will filter out extraneous incident infrared radiation during ambient processing are required.
U.S. Pat. No. 3,000,833, issued Sep. 19, 1961, discloses fluoren-9-ol salts represented by the formula ##STR1## which absorb more strongly in the near infrared relative to the corresponding basic triphenylmethane dyes represented by the formula ##STR2## which absorb more strongly in the visible range. This bathochromic shift (shift to the longer wavelength region) which occurs when the triphenylmethane compound is bridged to make the fluorene derivative is ascribed to the additional C-C bond as discussed in D. A. Brown and M. J. S. Dewar, J. Chemical Soc., 2134 (1954).
European Patent Application Publication No. 209259, published Jan. 1, 1987 and Japanese Patent Kokai No. 61-228986, Laid Open Oct. 13, 1986, disclose bridged phthalide derivatives of the formula ##STR3## which react with an electron accepting acidic material upon contact to produce color images which possess a strong absorption in the infrared range of 700-900 nm.
Thus, while many materials are known which absorb in the near infrared, pH-sensitive dyes having a colored or light-absorbing form above a given alkaline pH and a colorless or non-light-absorbing form below said pH and possess a strong absorption in the near infrared region (defined here as the region falling between approximately 700 nm and 1500 nm) are as yet unknown.